Recently, digital movie cameras have advanced so dramatically that it is expected that cellphones with a camera would achieve as high definition as an HDTV in the near future. However, if the size of an optical system or an image capture element were reduced significantly, then the basic performance of the imaging device would decline too much to maintain the minimum required level in terms of sensitivity or diffraction limit of lens. For that reason, such a high-resolution trend should hit a plateau sooner or later. Even so, however, the image quality can still be improved by compensating for the lack of image information of the object by computer graphics type processing. Nevertheless, for that purpose, pieces of physical information, including information about the three-dimensional shape of the object and information about the light source to illuminate the object, need to be collected during the image generation process. To obtain information about the shape of the object, an active sensor for projecting either a laser beam or a light beam emitted from an LED onto the object or a rangefinder system such as a differential stereo vision system is needed. However, such a sensor or system is not just bulky but also imposes various restrictions. For example, such a sensor or system allows a distance of at most several meters between the camera and the object. Besides, such a sensor or system cannot be used unless the object is a solid and bright diffusive object. Under such a restriction, the sensor or system cannot be used to shoot an object located at a distance outdoors or take a close up photo of a person with his or her hair and clothes shot as beautifully as possible.
To sense the shape of a completely passive object, polarization may be used according to some conventional technique. This technique takes advantage of the fact that the light reflected (which may be either specular reflected or diffuse reflected) from an object irradiated with non-polarized natural light will have various types of partial polarization due to geometrical factors such the surface direction and the viewpoint. To collect those sorts of information, however, the degrees of partial polarization of the respective pixels of the object should be obtained in the form of polarized images.
Non-Patent Document No. 1 discloses a camera that captures a moving picture while controlling a liquid crystal polarizer that is arranged in front of the lens of the camera. If such a camera is used, a color moving picture and information about the degrees of partial polarization of the object can be obtained in the form of images. However, this camera cannot obtain a single piece of polarization information until several frames are shot with the polarization main axes of the polarizer changed by applying a voltage to the liquid crystal layer. That is why a time lag of several frames is inevitable between the color image and the polarized image. In other words, these two images cannot be obtained at the same time. This technique is equivalent to a technique for rotating a polarizer with some mechanism.
Non-Patent Documents Nos. 2 and 3 disclose that a patterned polarizer with multiple different polarization main axes is spatially arranged in an image capture element in order to obtain light intensity images and images representing the degrees of partial polarization of the object. As the patterned polarizer, either a photonic crystal or a structure birefringence wave plate array may be used. According to these techniques, however, just a monochrome image and a polarized image can be obtained at the same time.
Patent Document No. 1 teaches arranging a polarization filter for some of G pixels in a Bayer color mosaic, thereby giving polarization property to a part of an image capture element and obtaining a color image and polarization information at the same time. According to this technique, an image with reduced specular reflection components is obtained from a color image. However, since a difference between two different polarization pixels is simply calculated, information about the degree of partial polarization of the object cannot be obtained perfectly.                Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 2006-254331        Non-Patent Document No. 1: Lawrence B. Wolff, “Polarization Vision: A New Sensory Approach to Image Understanding”, Image and Vision Computing 15 (1997), pp. 81-93, Elsevier Science B. V.        Non-Patent Document No. 2: Kawashima, Sato, Kawakami, Nagashima, Ota and Aoki, “Development of Polarization Imaging Device and Applications by Using Patterned Polarizer”, Institute of Electronics, Information and Communication Engineers of Japan, National Conference 2006, No. D-11-52, p. 52, March 2006.        Non-Patent Document No. 3: Kikuta and Iwata, “Polarized Image Measuring System”, Oplus E, Vol. 25, No. 11, pp. 1241-1247, 2003        